Differential gearing is well known and is used in many applications. Differentials are most commonly used in vehicle drive trains, and depending on the vehicle, are used to split torque between front and rear axle assemblies and/or left and right drive axles. When a differential is used to split torque between front and rear axle assemblies, it is normally termed an "interaxle differential." An inter-axle differential is normally connected to the front and rear axles by respective front and rear drive shafts.
In general, a differential includes a differential carrier which rotatably mounts confronting side gears which are connected to left and right vehicle axles when the differential forms part of an axle assembly or to front and rear drive shafts when used as an inter-axle differential. Two or more pinion gears are normally disposed between the confronting side gears and rotate on shafts that are carried by the carrier. A ring gear attached to the carrier is driven by an input pinion or input drive gear which produces rotation in the carrier and hence, an orbit-like motion in the pinion gears. As is well known, the motion of the carrier produces rotation in the side gears which, in turn, drive either left and right axles or front and rear drive shafts, depending on the application.
As is also well known in the art, a differential splits the input torque transmitted to the carrier (by the input pinion or input drive gear) between the left and rear axles or front and rear drive shafts, again depending on the application. If the side gears have equal numbers of gear teeth, the torque split is 50/50. For drive axle applications, a 50/50 torque split is generally desirable. However, in inter-axle applications, it is often desirable to have an unequal torque-split between front and rear drive axles. For example, in heavy off-road equipment, a 40/60 torque split between front and rear axles may be desirable. To achieve an unequal torque split, the side gears must have an unequal number of teeth, the ratio of the numbers of teeth on the side gears being directly proportional to the torque split that will be produced by the differential.
Currently, the most popular differential construction includes bevel side gears and associated bevel gear pinions. The use of bevel gears results in a durable and cost-effective differential. By virtue of its gear teeth configuration, a bevel gear differential cannot easily accommodate dissimilar side gears. In general, the side gears must be equally sized and include the same number of teeth in order for the beveled gear differential to operate properly. As a result, bevel gear differentials cannot normally produce an unequal torque split.
Differentials that use gears other than bevel gears have been suggested in the prior art. For example, U.S. Pat. Nos. 2,270,567 and 3,344,687 illustrate axle differentials that employ face-type side gears. When face-type side gears are used, the pinion gears carried by the differential carrier are usually configured as spur gears. U.S. Pat. No. 1,262,759 illustrates a differential gear that employs unequal face gears which are driven by two dissimilar pinion gears. The differentials suggested in these prior patents do not readily lend themselves to changes in the torque split produced by the side gears.